Co-genetic pegmatites associated with the granite of the Kawadgaon area in the Bastar craton, Central India, contain a wide range of ore minerals of Nb, Ta, Be, Sn, Zr, Ti, and REE, including columbite-tantalite, ixiolite, pseudo-ixiolite, wodginite, tapiolite, microlite, fersmite, euxenite, aeschynite, beryl, cassiterite, monazite, xenotime, zircon, ilmenite, triplite, and magnetite. There is a distinct vertical zonation between the rare metal and tin pegmatites in apical parts of the host granite. Geochemically, these are LCT-S type, beryl-columbite-phosphate pegmatites that have notably high contents of SiO2 (av. 73.80%), Rb (av. 381 ppm), and Nb (av. 132 ppm). The investigated granites probably were derived from the melting of older crustal rocks, as indicated by a high initial 87Sr/86Sr isotopic ratio, and the major-element geochemistry of the granites and pegmatites. Plots of mol. CaO/(MgO+FeOt) vs. mol. Al O /(MgO+FeOt) suggest that the source rock was pelitic metasediments. Based on the available data, it is postulated that the derivation of pegmatites from the parent granite occurred shortly after granite emplacement in the late Archaean-early Proterozoic (∼2500 Ma). The K/Rb, Ba/Rb, and Rb/Sr ratios of the felsic bodies reveal that a substantial part of the granite formed from evolved melts, and further fractionation produced the co-genetic pegmatites and associated rare metal and rare earth deposits.

The results of geochronological studies on columbite-tantalite and monazite from the rare metal pegmatites of the Kawadgaon – Challanpara area in Bastar craton, central India are presented. Columbite-tantalite yielded U-Pb concordia upper intercept age of 1978±16 Ma (MSWD = 0.18). Radiogenic 207Pb*/206Pb* (T7/6) ages on 4 out of 5 columbite-tantalite vary in a narrow range of 1903 to 2077 Ma and are similar to U-Pb age, whereas, one sample shows younger 207Pb*/206Pb*(T7/6) age of 1728 Ma. Younger Pb-Pb age of 1744 ± 250 Ma (MSWD = 150) has also been indicated by these columbite-tantalite samples. Four out of five monazite samples define Pb-Pb errorchron age of 2050±370 Ma (MSWD = 165) and radiogenic 207Pb*/206Pb* (T7/6) ages on 3 out of 5 monazites show a narrow range of 1983 to 2083 Ma. Other two samples show younger 207Pb*/206Pb*(T7/6) ages as 1254 Ma and 1592Ma. Both monazite and columbite-tantalite indicate disturbance in Pb and U isotopic systematics as revealed by high MSWD. However, selected samples from both monazite and columbite-tantalite indicate age of their formation as c. 2000 Ma. Younger ages, i.e., 1254 to 1744 Ma are indicative of later geological disturbances. Reported age of c. 2000 Ma is comparable to Rb-Sr date of pegmatitic muscovite (1850-2330 Ma) from this area and is younger to intrusive granites of c. 2500 Ma. By analogy, therefore, it may be inferred that the age of the rare element mineralization may be ∼2000 Ma old, and linked with younger granitic activity that spanned over the period from 2300 to 2100 Ma in the Bastar craton.

We report a new occurrence of thorianite from syenitic pegmatite near Bhaluchuan, Sambalpur district, Odisha. The thorianite is brown to deep-brown with round grains of 2 to 10 mm size. The chemical analysis of the investigated thorianite reveals 64.8% ThO2, 25% U3O8, 3.81% PbO and 1.7% Fe2O3. Calculated structural formula of the thorianite is (Th+40.61U+40.14U+60.08ΣREE+30.017Pb+20.04Ca+20.01Mn+20.001Fe+30.05Al+30.003Sc+20.002K+10.005Na+10.008Si+40.04Ti+40.02)O2.08. Chondrite-normalised rare-earth element (REE) plot of the thorianite reveals enrichment of light REE (LREE) over heavy REE (HREE) with pronounced negative Eu-anomaly (Eu/Eu* = 0.35). The (ΣLREE/ΣHREE)N ratio is perceptibly high (2.76). The (La/Lu)N (42.31), (La/Yb)N (27.49) and (Ce/Yb)N (21.58) ratios are also very high. X-ray diffraction (XRD) pattern of the investigated thorianite displays sharply-defined reflections. Corresponding interplanar spacings (d-spacings) of all the reflections are in very close agreement with those published for thorianite standard in International Centre for Diffraction Data (ICDD) Card No. 4-556. However, I/Io of two reflections (1.9694Å and 1.6787Å) are lower than those published for thorianite standard. The unit cell parameter (ao) of the investigated thorianite (ao 5.5750Å) is also less than ao of thorianite standard (ao 5.6000Å and V 175.62Å3), which is because of extensive substitution of Th by U.

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